Former top executives at defunct law firm Dewey & LeBoeuf, including chairman Steven Davis, conspired to falsify income statements in an attempt to forestall its collapse in 2012, the firm’s former finance director testified Monday. Francis Canellas, a key prosecutorial witness at the criminal trial of Davis, executive director Stephen DiCarmine and chief financial officer Joel Sanders, said all three were aware of improper accounting tricks intended to fool auditors about Dewey’s true financial state.